ABUNDANCE AND COMPOSITION OF PRECIPITATION FEATURES ON WEST ANTARCTIC SUBGLACIAL TILL GRAINS

Previous work conducted on sediment samples from under the Whillans Ice Stream (WIS) in West Antarctica has shown the presence of a viable and robust microbial community (Christner et al. 2014). More recently we have found that dissolution pitting and precipitates are very common on sand-sized quartz grains. Given the geochemical energies in subglacial environments we have considered that these surface features occurring on freshly fractured grain surfaces may well mean that microbially-mediated chemical weathering is likely occurring widely under the WIS. Feldspar minerals possess many more elements useful as nutrients for chemoautotrophs than quartz, and should serve as a better foundation for the microbially-mediated chemical weathering. This study identifies the abundance and composition of possible biogeochemical precipitation features on feldspar sand-sized grains. Samples for this study come from three field sites; one near the end of the WIS (Subglacial Lake Whillans (SLW)) and the other two farther up the ice stream, at sites called “UpB”. The abundance of distinctive precipitation features are described using a Scanning Electron Microscope and the chemical composition of each host grain and its precipitate were obtained using an energy-dispersive X-ray spectroscope (EDS). The precipitation features are composed of carbon. Data from the two sites show an increase in precipitation features both with increasing grain size and with decreasing depth. There is no statistical difference in abundance between sites, although we have fewer samples from UpB.